1. Field of the Invention
The present invention relates to an apparatus and method that measure the optical performance of an optical element, and more particularly to a measuring apparatus and method used for an exposure apparatus of a step-and-repeat manner, a step-and-scan manner, etc. for manufacturing devices, e.g., semiconductor devices such as ICs, LSIs, etc., image pick-up devices such as CCDs, etc., and display devices such as liquid crystal panels, etc. The present invention is also directed to an exposure apparatus and method using the measuring apparatus and method, and a device manufacturing method.
2. Description of Related Art
The recent fine processing increasingly requires a projection exposure apparatus to improve the resolving power. A higher numerical aperture (“NA”) of a projection optical system is effective to the improvement of the resolving power, and the projection exposure apparatus should precisely transfer a mask pattern onto a wafer at a predetermined magnification (or a reduction ratio). This requirement is met through use of a projection optical system that has good imaging performance and little aberration. Since the minimum critical dimension or resolution transferable by the projection exposure apparatus is in proportion to the exposure light's wavelength, use of a shorter wavelength makes the resolution finer. Thus, the recent demands for finer processing to semiconductor devices promote a shorter wavelength from the ultra-high pressure mercury lamp (i-line having a wavelength about 365 nm) to a KrF excimer laser having a wavelength about 248 nm, an ArF excimer laser having a wavelength about 193 nm, and even extremely ultraviolet (“EUV”) light having a wavelength between 10 nm and 15 nm. In this context, the measuring apparatus is required to accurately measure the aberration of the projection optical system in the exposure apparatus.
A method for measuring the aberration of the optical system includes, for example, a Hartmann test, and a method that utilizes interference. See, for example, Japanese Patent Application, Publication No. 2000-97666 and U.S. Pat. No. 6,312,373. Here, a brief description will be given of an illustrative measuring apparatus 1000 that utilizes a shearing interferometer.
The measuring apparatus 1000 includes, as shown in FIG. 9, a dedicated mask 1010, a target optical system 1020, an optical element 1030 having a beam splitting function, and an image detector 1040, such as a CCD. The dedicated mask 1010 generates an aplanatic spherical wave from the light emitted from a light source (not shown), and the aplanatic spherical wave enters the target optical system 1020. The light incident upon the target optical system 1020 is emitted with an aberration of the target optical system 1020, and enters the optical element 1030. The optical element 1030 is a diffraction grating, and splits the incident light into plural orders of diffracted lights. At least two orders of diffracted lights enter the image detector 1040. The image detector 1040 detects a shearing interference fringe, which occurs when two wave fronts split by the optical elements 1030 laterally offset and superimpose on each other. The shearing interference fringe contains information of the aberration of the target optical system 1020, and provides the wave front shape of the target optical system 1020 through integrations.
When the optical element 1030 as the diffraction grating is replaced with a Hartmann plate, the wave front is measured in accordance with the Hartmann test. The Hartmann plate is a light shielding plate having plural holes. The light incident upon the Hartmann plate is split into plural rays after passing the holes, and enters the image detector 1040. Since an incident position of each ray upon the image detector 1040 varies according to the optical performance (or aberration) of the target optical system 1020, the incident position of each ray detected by the image detector provides the wave front shape of the target optical system 1020.